The Foreign Office has turned down a request from the Ecuadorian government to grant the WikiLeaks founder, Julian Assange, diplomatic status as a means of breaking the stalemate over his continued presence in the UK.

The development comes amid reports that Assange – an Australian who has been holed up in the Ecuadorian embassy for more than five years – has recently become a citizen of the South American state.

If awarded the status of a diplomat, it is thought, Assange could obtain certain rights to legal immunity and might be able to leave the embassy in Knightsbridge, and eventually the UK, without being arrested for breaching his former bail conditions.

Swedish prosecutors last year unexpectedly dropped their investigation into allegations against him, which included a claim of rape. He had been resisting extradition to Stockholm for years.

Assange still faces arrest for breaching bail conditions if he steps outside the embassy. WikiLeaks has voiced fears that the US will seek his extradition if he leaves the embassy. It is rumoured that there is a sealed US indictment ordering his arrest.

An FCO spokesperson, confirming the latest attempt to resolve the impasse, said on Wednesday night: “The government of Ecuador recently requested diplomatic status for Mr Assange here in the UK. The UK did not grant that request, nor are we in talks with Ecuador on this matter. Ecuador knows that the way to resolve this issue is for Julian Assange to leave the embassy to face justice.”

At the same time Assange appeared on his Twitter account for the first time wearing an Ecuadorian national football shirt.

There were reports in newspapers in Quito that he had recently been granted a national identity number. On Wednesday, the Reuters news agency reported it had found an entry for “Julian Paul Assange” in Ecuador’s Civil Registry, which only includes Ecuadorian citizens.

Earlier this week Ecuador’s foreign minister, María Fernanda Espinosa, said her country was seeking a “third country or a personality” to mediate a final settlement with the UK to resolve the impasse and that it was “considering and exploring the possibility of mediation”.

“No solution will be achieved without international cooperation and the cooperation of the United Kingdom, which has also shown interest in seeking a way out,” she told foreign correspondents in Quito, according to Agence France-Presse.

Assange, who has received numerous visitors to his modest quarters in the embassy, ranging from Nigel Farage to Lady Gaga, has described the period since his initial arrest as a “terrible injustice”. Not being able to see his children grow up was “not something I can forgive”, he said.

For several years, Metropolitan police officers maintained a constant watch of the embassy, which is situated behind Harrods in central London, at a cost of at least £11.1m, according to figures released by Scotland Yard in June 2015. Four months later, police lifted the round-the-clock guard on the basis it was no longer proportionate.

A United Nations panel concluded in 2016 that Assange was under arbitrary detention.